Laccase catalysed oxidation of syringic acid: calorimetric determination of kinetic parameters.

Isothermal titration calorimetry (ITC) was used to study the oxidation of syringic acid by laccases from two different sources: Galerina sp. HC1 and Trametes versicolor. Total molar heat of reaction with both enzymes was similar (230 kJ/mol for Galerina laccase and 233 kJ/mol for Trametes laccase), and was independent of syringic acid concentration. The kinetic parameters of the reaction were calculated from the single injection assay by applying the nonlinear least squares fitting (NLSF) of experimental data to the Michaelis-Menten equation. Higher values for V(max) were obtained with Galerina sp. laccase, whereas K(m) values were comparable for the two enzymes.